This invention relates to heat exchanger fins and more particularly relates to such fins in folded form made from a strip of metal foil or sheet. The invention includes not only the folded fin itself but the method and apparatus for its manufacture.
Heat exchanger folded fin material is known to those skilled in the art as well as methods and apparatus for its manufacture. Such material and a method and apparatus for its manufacture are for example described in U.S. Pat. No. 3,766,873, incorporated herein by reference. U.S. Pat. No. 3,766,873 describes an apparatus wherein a strip of metallic material is fed between cutting rollers where a series of fin patterns are cut into the strip and the strip is subsequently fed to star shaped folding rollers where the strip is folded into a serpentine heat exchange fin.
Unfortunately, fins made using the apparatus, described in U.S. Pat. No. 3,766,873, are not of high enough quality for many applications. In particular, the folds are not as uniform as desired in that the arc of the fold near the fold apex and beyond, are frequently asymmetrical and distances between folds are often not as uniform as desired. Such effects are not only unaesthetic which can result in a marketing disadvantage, but cause a reduction in product quality from a performance point of view. Unequal distances between folds and asymmetric folds adversely affect the uniformity of fold height, which can in turn affect fluid flow around and through the fins and make it difficult to solder the fin to a base at each apex on a side of the fin and even if accomplished, will create a distorted fin shape.
It is known that a fairly uniform fin having a symmetrical fold arc and a fairly uniform fin height can be made using a costly and difficult to manufacture rotating fin shaping apparatus wherein the louvres are cut and formed and the bends are made simultaneously. Such a fin shaping apparatus comprises two intermeshing star shaped rollers where the surfaces represented by the legs of the points of the star have machined louvre cutting and forming blades. Such star shaped rollers having cutters on their surfaces, due to the complex and difficult machining operations required for their manufacture, are exceedingly costly, often twenty thousand dollars or more. Furthermore a separate set of such rollers is required for each change in louvre shape or fold distance.